1. Technical Field
The present invention relates to gas turbine engines, and in particular, to devices for sampling turbine exhaust emissions.
2. Description of the Related Art
Gas turbine engines are commonly used in power generation and propulsion applications. Generally, gas turbine engines have a set of rotating turbine blades that compress air leading to one or more combustors into which fuel is injected and ignited. Fuel is delivered through metering orifices to burners in the combustors under pressure through a fuel line. Combustion of the fuel turns one or more sets of turbine blades, used for energy extraction or propulsion, and which can be used to drive the compressor blades.
Gas turbine engines are the main source of new power generation. To meet the rising energy demands, power plants operate the turbine engines essentially continuously. The byproducts of combusting hydrocarbon fuels, such as coal, include sulfur oxides (SOx), such as sulfur dioxide, carbon oxides (COx), such as carbon monoxide and carbon dioxide, and nitrogen oxides (NOx), such as nitric oxide. These byproducts, particularly NOx, have been thought to play a role in a wide variety of health and environmental issues including smog, acid rain and global warming.
These health and environmental concerns have prompted the Environmental Protection Agency and local legislators to promulgate emission standards for power plants. To meet the emission standards, low NOx combustors were devised which provide staged combustion to limit the amount of air in the initial stages of combustion when fuel bound nitrogen is released and also to reduce the flame temperature during some phases of combustion. Many power plants have also converted to using gas turbines that burn natural gas for sustained operation after being ignited by a fossil fuel, such as liquid diesel fuel. Natural gas burns cleaner than fossil fuels, with significantly lower NOx and COx emissions.
However, as emission standards become increasingly stringent with regard to SOx, COx and NOx, as well as other post-combustion components, such as mercury, control of emissions remains a significant issue. Not only are power plants being held to strict emissions standards, it is becoming increasingly common for the emissions to be monitored continuously, using either a Predictive Emissions Monitoring System (PEMS), which uses an algorithm to model various exhaust emissions components based on turbine operating parameters such as fuel consumption and certain ambient conditions, or a Continuous Emissions Monitoring System (CEMS). A CEMS uses actual samples of turbine exhaust to analyze and record pertinent emission contents. CEMS analyzers are commercially available from K2BW Environmental Equipment Services, Company of Willow Grove, Pa.
For the CEMS, an electronic analyzer device is coupled to the gas turbine exhaust. One or more valves may be placed in-line with turbine exhaust line(s) to shut-off flow to the analyzer should monitoring need to be discontinued, for example, during engine shut down or to service the analyzer. These shut-off valves are typically manually controlled, however, it would be feasible to incorporate an electronically controlled valve to automate the exhaust shut-off to the analyzer. However, the exhaust environment of conventional industrial gas turbines is rather extreme, typically in the range of 1,200-1,300° F. and laden with particulate matter, such that conventional valving is typically unsuitable.
Moreover, the conventional CEMS is designed to provide emissions readings for the pertinent constituent parts of the exhaust for the turbine overall. However, many gas turbines have multiple discrete combustion zones. For example, the large industrial gas turbines used in modern power plants today typically have 14-16 annular combustion zones or combustor cans, each having a dedicated burner nozzle and fuel supply line. The gas turbine may operate with fuel burning in all or only a portion of the combustion zones depending on the power demand and other factors. Thus, it may be desirable to close off one or more exhaust outlet lines corresponding to inactive combustion zones of the turbine, while leaving the exhaust lines corresponding to the fired zones open. It may also be desired to selectively analyze exhaust from one or a select number of operating combustion zones. Further, it would be desirable to use the data from the emissions analysis as feedback for the turbine combustion performance, at one or more of the combustion zones, for example to pinpoint a high NOx emission combustor or a problem with one or more of the burner nozzles.
Since conventional systems do not provide suitable valving to achieve the desired control of turbine exhaust sampling, an improved emissions sampling valve is needed.